This invention relates to nuclear reactors which are fuelled with ceramic fuel, that is, nuclear fuel comprising one or more compounds such as an oxide or carbide of a fissile metal or metals (and of a fertile metal for breeding where applicable). The invention has particular reference to expedients known in the art as `core catchers`, which serve to catch and disperse the fuel constituting the reactor core as a safeguard against operation under extreme and emergency conditions such that a melt down of the fuel occurs. A typical example of fuel for which such a core catcher would be provided is mixed plutonium/uranium oxides such as is used in a gas cooled fast reactor.
The problems associated with the core catchers include dispersing the molten fuel debris to avoid criticality and in addition removing as much heat as possible from the dispersed melt, firstly, to avoid boiling of the fuel melt which would release fission products and plutonium aerosols, and secondly to bring about solidification of the molten debris to prevent its penetrating the reactor containing vessel. Ceramic nuclear fuels are notoriously poor heat conductors which exacerbates the problem. Therefore dispersion into as many small volumes as possible is desirable. Yet another problem resides in the avoidance of premature solidification of molten fuel in the upper region of the core catcher. If such a condition should occur upward radiation of heat from the melt could cuase serious damage to the remaining reactor components and thermal insulation therefore it is an object of the invention to provide a ceramic fuelled nuclear reactor having a core catcher which, in addition to dispersing a fuel melt into numerous small valumes, also reduces the tendency for premature solidification of fuel melt in the upper regions.